24-06-2023, 09:40 PM
Hi Dave
I found a photo online of VB 476, a similar car. I won't post it for copyright reasons, but comparing its tailpipe size to the 3 1/2 inch high numberplate letters I make its Tail Pipe one inch internal diameter.
At an estimated volumetric efficiency of 80%, at 2000 RPM the engine will be flowing a modest 53 cubic feet per minute and the tailpipe gas velocity will be 109 mph. Probably not too much of a restriction, from memory even the 48 BHP Morris Minor of the 1960's had a "pea shooter" exhaust.
Using a typical value of 0.5 lb of petrol per BHP-hour and 20 BHP, that's 1.35 gallons per hour e.g. 33 mpg at 45 mph. So it would seem there is some room for improvement !
I found a photo online of VB 476, a similar car. I won't post it for copyright reasons, but comparing its tailpipe size to the 3 1/2 inch high numberplate letters I make its Tail Pipe one inch internal diameter.
At an estimated volumetric efficiency of 80%, at 2000 RPM the engine will be flowing a modest 53 cubic feet per minute and the tailpipe gas velocity will be 109 mph. Probably not too much of a restriction, from memory even the 48 BHP Morris Minor of the 1960's had a "pea shooter" exhaust.
Using a typical value of 0.5 lb of petrol per BHP-hour and 20 BHP, that's 1.35 gallons per hour e.g. 33 mpg at 45 mph. So it would seem there is some room for improvement !